Natural coagulants for appropriatewater treatment: a novel approachby J.P. Sutherland, G.K. Folkard and w.o. Grant

evaluation has highlighted problems inturbidity removal at low initialturbidities. With respect to thebacterial work, reductions in bacteriaof between 90 to 99.9 per cent havebeen achieved.Attempts to isolate the 'active

ingredient' of M.Stenopetala havebeen made. Findings indicate that twowater-soluble proteins (approximatemolecular weight 8,000 Daltons) areresponsible for the coagulationprocess, and purification has resultedin a freeze-dried extract of the water-soluble seed material. Work with theextract has shown that significantlylower dosages are required to give anequivalent performance to the wholeseed in the reduction of both bacteriaand turbidity. Investigations into theeffect of the extract on bacteriophage(bacterial viruses) have also beencarried out. An important finding isthat not only is effective removal ofbacteriophage possible, but the extract

Laboratory evaluationThe efficiency of whole-seedsuspensions of M.Stenopetala andM.Oleifera was determined usingmodel clay (Kaolin Light, BDH Ltd),clay/bacteria and diluted sewagesuspensions. Results have shown thatboth seed types are effective atremoving turbidity from waters withhigh initial turbidities. The laboratory

traditional usage has been promotedover recent years in areas of Indonesia,South America and North East Africa.As an alternative to chemicaltreatment their use has manyadvantages including the low cost,ease of use and ready availability.

John P. Sutherland is a Research Assistant,Geoffrey K. Folkard a Lecturer in theDepartment of Engineering, and William D.Grant a Senior Lecturer in the Department ofMicrobiology at The University of Leicester,LEt 7RH. Surface sources are often highly turbid during the rainy season.

Recent field trials in Malawi haveproved the viability of using indigenousMoringa seeds to clarify turbid waters.

IT HAS BEEN ESTIMATED that ofthe 1200 million people who arewithout safe drinking-water, some 80per cent live in relatively small ruralcommunities. In most situationsvillagers draw water for drinking fromsurface sources. For a riparianpopulation in the rainy season, thesesources are highly turbid and onoccasions contain bacterialconcentrations similar to that of weakraw sewage.

Against this background, small-scale and household water-treatmentsystems have an important role to playin providing aesthetically pleasing andbacteriologically safe drinking-water.Chemical treatment of surface waters,using for example aluminium sulphate(alum), is generally prohibitivebecause of the high cost, the lack ofskilled workers needed for itsapplication, and the uncertainty of thequantity and quality of supplies. Theuse of slow sand filters as analternative has met with some success,but there are the problems of the initialcost and the continuous maintenance.Furthermore pre-settlement isnecessary for higher turbidities.In an attempt to find a cheap and

simple method of treating surfacewaters, attention has been focused onthe use of natural substances asprimary coagulants for the removal ofsuspended organic and inorganicmatter. The clarifying powers ofnatural substances are well known inmany remote areas of the developingcountries and, indeed, their use hasbeen traced back 4,000 years. Seedsuspensions of Moringa Oleifera andM. Stenopetala have been used formany centuries in the Sudan and this

30 WATERLINESVOL.8 NO.4

appears to have an inhibitory effect,preventing replication of thebacteriophage. Further investigationsof this effect are being carried out. AbaChem Engineering Ltd.

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out. Sometimes confirmatory water-quality analysis was carried out byBWB. Total counts and presumptivecoliform counts were carried out usingthe Paqualab portable membrane-fIltration and incubator apparatus.The effectiveness of M.Oleifera

and M. Stenopetala as whole seedadditions were examined for allwaters, and then these results werecompared with those obtained foralum. Preliminary work was carriedout using the freeze-dried extract ofthe M.Stenopetala; previous workindicated that the extract wouldrequire lower dosages than the wholeseed to achieve equivalentclarification. In fact, although efficientclarification was achieved, the dosesrequired were considerably higher thanfor the whole seed. This was atvariance with data obtained previouslyfor laboratory suspensions. Thereasons for this phenomenon are as yetunknown, although it is possible thatthere were problems with productionscale up and storage.

Co-coagulationAs a result of the problems associatedwith the use of the extract a novelapproach was tried in whichapproximate equal concentrations ofalum and M.Oleifera whole seed were

Blantyre Water Board (BWB) and theMinistry of Works and Supplies(MWS), it was decided that samplingwould take place at Walker's Ferrytreatment plant, under the control ofBWB, and at Mwanza and Thyolowater-treatment plants, under thecontrol of the MWS.From each water source a 40 litre

sample was collected. Beforelaboratory testing, basic water-qualityanalysis of the raw waters was carried

Field studyThe principle aim of the field studywas to evaluate the performance of thechosen natural coagulants in theflocculation of the turbid waterstypically experienced in the rainyseason.The coagulants investigated were

seeds of the trees M.Stenopetala, ofKenyan origin, and M.Oleifera, ofMalawian origin. Information gatheredfrom the National Herbarium ofMalawi indicated that the growth ofM.Oleifera was widespread throughoutthe country. In Chichewa, the nationallanguage of Malawi, the tree is calledchamwamba. The trees are grown toprovide saplings for 'live' fences andpods for consumption. Villagers usethe leaves, flowers and immature podsin a relish called ndiwo. Mature greenpods were found on sale in one of theBlantyre markets, and it was learntthat the Asian population use the podsas vegetables. Despite the widespreadgrowth, the seeds are not used atpresent for traditional water-clarification purposes. Seed suppliesfor testing were obtained from treesgrowing outside the Great Hall ofChancellor College, Zomba.Raw-water sampling sites were

identified bearing in mind two maincriteria. Firstly, the rivers andcatchment areas should be as differentfrom each other as possible, andsecondly, the travelling distance to thesource from the polytechnic was to bekept to a minimum. Followingdiscussions with representatives from

The pods (left), leaves (centre) andfruit ofMorlnga Oleifera. (DiagramfromCommon Trees of Puerto Rico and the VIrgin Islands, Little and Wadswort,WashingtonDC, USA,1964)

WATERLINESVOL.8 NO.4 31

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CONSALLEN INNOVATIVEHANDPUMPS

would promote the introduction of theseeds for rural applications. Theintroduction of the seeds for large-scale treatment is considered viable.The limited bacterial data has

indicated that alum is more effective atremoving bacteria from raw waters.However. because of problemsencountered with the analysis, no firmconclusions can yet be drawn.The main thrust of new work, againfunded by the aDA, will be thepractical introduction of M.Oleiferaseeds. either in whole-seed or extractform, to existing low-volumetreatment works in Malawi as co-coagulants with alum.This work will include cultivation

on an appropriate scale. thedevelopment of a cost effectivemethod of seed processing andstorage, an investigation of the activeseed constituents on microbial andviral activity, and the feasibility ofgene cloning.

ACknowledaementThe authors wiSh to acknowledge thefinancial assistance given by the OverseasDevelopment Administration, and the co-operation and assistance of the Polytechnic ofMalawi, the Ministry of Works and Suppliesand Blantyre Water Board without whom thisproject would not have been possible.

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Now available, a combined handpump and borehole forinstallation directly into a suitable drilled hole. No risingmain is employed with this extractable system.

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co-coagulation gives dramaticimprovements in flocculation abilityand floc characteristics even at lowturbidities. The procedure generatesfloc formation and settling ratessimilar to alum although. unlike alum.the floc produced using this systemhave a more uniform size. This resultsin even settling and a reduced sludgevolume following settling. Further it isbelieved that this uniformity of sizewould lead to more effective flocblanket formation in upward flowclarification. The results obtained haveshown that significant reductions inalum usage in the range 50-80 per centcan be made using the co-coagulationprocedure. At high turbidities the ne¢for alum may be eliminated. the wholeseed giving equivalent or betterperformance. For many developingcountries, imported alum is the majorcost element in the provision ofpotable water. Malawi currentlyspends in excess of £220,000 perannum on importing alum. The use ofthe seeds. either alone or inconjunction with alum. for the large-scale treatment of raw waters wouldhave two main implications. Firstly.the provision of a renewable naturalresource that would reduce bothforeign exchange expenditure and thedependency on foreign supplies.Secondly, success on the large scale

A renewable naturalresourceThe use of M.Oleifera in conjunctionwith alum to produce an effect termed

mixed together and used as thecoagulant. Although investigationsinto the use of M.Oleifera as acoagulant aid have been previouslycarried out the observed effects of theabove procedure do not appear to lendthemselves to the traditional theoriesconcerning coagulant-aid systems. Asa result the procedure has been termedco-coagulation. Experiments tooptimize the co-coagulant procedurewere based on preliminarydetermination of optimum alum doseand subsequent use of M.Oleifera andalum to produce maximum savings inthe concentration of the latter.The results using whole-seed

suspensions on raw waters have showngood correlation with those obtainedfor model suspensions. Both seedtypes gave equivalent, and in somecases superior performance to that ofalum in the clarification of highlyturbid waters. Additionally. flocformation and settling rates observedat high turbidities were similar to thosefor alum. For the Thyolo source water.with an initial turbidity of 150 NTU,coagulation with doses of 40mg/l ofeither alum or moringa seed resulted inturbidities of about 10mg/l. Similarresults were obtained by co-coagulation with 15mg/l alum plus25mg/l moringa seed. There was anunusual alum response here which isconsidered to be a result of the pHdependency of alum coagulation.Increased doses of alum gaveincreased turbidities, unlike the seeds,thus indicating an advantage of usingthe seeds.For the Mwanza source water. with

an initial turbidity of 1800 NTU.coagulation with doses of 75mg/l ofeither alum or moringa seed resulted inturbidities under 10mg/I. Co-coagulation with 25mgll alum plus50mg/l moringa seed gave turbiditieswell under lOmg/l.Results for low-turbidity waters

indicate a limit to the effectiveness ofseed usage alone. For Mwanza andThyolo low-turbidity samples.flocculation occurred but the floesformed were small and light and didnot settle quickly. These fmdings agreewith previous work.3 However, for theWalker's Ferry sample the floesformed were large and relatively fastsettling, contiary to previous findings.It is believed that the higher ioniccontent of the Walker's Ferry samplewould account for this.

32 WATERLINESVOL.8 NO.4